1. Field of the Invention
The present invention relates to a light combining method for combining light from multiple light sources, an illumination device, and a projection display device incorporated with the illumination device.
2. Description of the Related Art
Heretofore, there has been known a projection display device (hereinafter, called as a “projector”) for modulating light from a light source based on an image signal to project modulated image light onto a projection plane.
High luminance has been required in the projector, as large-sized screens have been produced in recent years. High luminance has also been required in an illumination device to be loaded in the projector.
In the illumination device, an arrangement of combining light emitted from multitudes of light sources by using a mirror or a like device may be employed. The above arrangement is advantageous in enhancing light integration, and producing an illumination device with high luminance.
For instance, multiple light sources are arranged on each of a first plane and a second plane opposing to each other, and a third plane orthogonal to the first plane and the second plane. A mirror corresponding to the light sources arranged on the first plane and the second plane is provided, in a space defined by the first through the third planes, at such a position that light from the light sources arranged on the third plane may not be interrupted. Light from the light sources arranged on the first plane and the second plane is respectively reflected on the mirror in the same direction as the propagating direction of light from the light sources arranged on the third plane. In this way, illumination light obtained by combining the light in three directions is emitted from the illumination device.
In recent years, an LED light source or a laser light source is used as a light source to be provided in the illumination device. The laser light source is superior in rendering a wide color space with high luminance and high precision. With use of the laser light source, production of an illumination device with higher luminance can be expected.
However, the total heat generation amount of a laser light source is large, as compared with a lamp, and a temperature-dependent output change is likely to occur. In view of this, various methods for cooling a laser light source may be proposed. For instance, a laser light source may be cooled by using a heat sink (heat releasing fin), a Peltier element, or a liquid cooling system.
In the case where an edge emitter semiconductor laser is used as a laser light source, the solid angle of emission beams is considerably large. Accordingly, it is necessary to collimate laser light into parallel light, according to needs, by a lens such as a cylindrical lens in order to smoothly guide the laser light to an optical system (such as a fly-eye lens) provided posterior to the lens. In this case, the lenses to be arranged on each of the first plane, the second plane, and the third plane may be integrally formed into an optical element. The optical element (hereinafter, called as “lens array element”) constituted of the multiple lenses is arranged on each of the first plane, the second plane, and the third plane.
In the case where a cooling portion is mounted on each of light sources, as described above, the size of each of the light sources may be increased, and the light sources are likely to interfere with each other. Accordingly, it is difficult to arrange each two of the light sources close to each other on each of the planes. Also, in the case where a lens such as a cylindrical lens is used, if the lens arrangement is different among the planes, it is necessary to prepare different lens array elements for these planes, which may increase the cost.
However, it is not easy to provide a light source arrangement, wherein each two of the light sources are not arranged close to each other, and identical lens array elements are used for the three planes. In the case where light integration is increased, and the number of light sources to be arranged on each of the planes is increased, it becomes increasingly difficult to obtain the above light source arrangement.